Less is More: Treatment with BTH and Laminarin Reduces Herbivore-Induced Volatile Emissions in Maize but Increases Parasitoid Attraction

Abstract

Chemical plant strengtheners find increasing use in agriculture to enhance resistance against pathogens. In an earlier study, it was found that treatment with one such resistance elicitor, BTH (benzo-(1, 2, 3)-thiadiazole-7-carbothioic acid S-methyl ester), increases the attractiveness of maize plants to a parasitic wasp. This surprising additional benefit of treating plants with BTH prompted us to conduct a series of olfactometer tests to find out if BTH and another commercially available plant strengthener, Laminarin, increase the attractiveness of maize to three important parasitic wasps, Cotesia marginventris, Campoletis sonorensis, and Microplitis rufiventris. In each case, plants that were sprayed with the plant strengtheners and subsequently induced to release volatiles by real or mimicked attack by Spodoptera littoralis caterpillars became more attractive to the parasitoids than water treated plants. The elicitors alone or in combination with plants that were not induced by herbivory were not attractive to the wasps. Interestingly, plants treated with the plant strengtheners did not show any consistent increase in volatile emissions. On the contrary, treated plants released less herbivore-induced volatiles, most notably indole, which has been reported to interfere with parasitoid attraction. The emission of the sesquiterpenes (E)-β-caryophyllene, β-bergamotene, and (E)-β-farnesene was similarly reduced by the treatment. Expression profiles of marker genes showed that BTH and Laminarin induced several pathogenesis related (PR) genes. The results support the notion that, as yet undetectable and unidentified compounds, are of major importance for parasitoid attraction, and that these attractants may be masked by some of the major compounds in the volatile blends. This study confirms that elicitors of pathogen resistance are compatible with the biological control of insect pests and may even help to improve it.

The prospect of applying chemical elicitors and plant strengtheners to enhance the biological control of crop pests

“…Previous experiments revealed minor changes in constitutive volatile emission of BTH-or laminarin-treated, undamaged maize plants, but surprisingly some herbivore-induced volatiles were found to be suppressed after treatment [61,65]. This study confirms this suppression, both in the case of foliar and seed application of the plant strengtheners ( figure 3).…”

“…The initial study by Rostás & Turlings [61] was followed up by Sobhy et al [65], who tested BTH, as well as another chemical plant elicitor, laminarin, which induces the accumulation of phytoalexins and expression of a set of pathogenesis-related proteins [66] through the activation of the SA pathway [67]. The aim was to find out whether treatment with these plant enhancers has a general positive effect on the attractiveness of plants to parasitoids.…”

“…Newly hatched larvae were reared in transparent plastic boxes on a wheat germbased artificial diet until they had reached the second instar, at which point they were used for experiments. The larval endoparasitoids, M. rufiventris Kok., Cotesia marginiventris (Cresson; Braconidae: Hymenoptera) and Campoletis sonorensis (Cameron; Ichneumonidae: Hymenoptera) were reared as described in Sobhy et al [65]. Thirty minutes before the bioassays, cages with 2 -4 day old parasitoid adults were transferred to the laboratory for acclimatization.…”

“…The volatiles were identified by comparing their mass spectra with those of the NIST05 library and by comparing their retention times with those of previous analyses [38,65]. The total emission for each compound rstb.royalsocietypublishing.org Phil.…”

Prohydrojasmon treatment of lima bean plants reduces the performance of two-spotted spider mites and induces volatiles

“…Interestingly, neither predator showed any preference for JAtreated leaves over uninfested leaves (Shimoda et al 2002). Sobhy et al (2012) reported that BTH increased the attractiveness of host-infested maize plants to a parasitic wasp. Taken together, these findings suggested that the behavior/performance of TSSMs and their carnivorous natural enemies could be manipulated by using PDJ and BTH, which are functional analogs of JA and SA, respectively, as a method of biological control of TSSMs.…”